The present invention relates to electronic adjustments and, in particular, to circuitry for providing a variable signal.
In many electrical and electronic equipment periodic adjustments are necessary. For example, the exciter of a broadcast station needs to be periodically adjusted to set the modulation percentage and the overall power output. In a typical situation depicted in FIG. 1, a video or audio signal is applied across potentiometer P1. The wiper of potentiometer P1 is connected to modulator 10 whose output is delivered to an IF amplifier 12. The IF amplifier has a control terminal C that can receive a variable, gain-controlling signal. Variation of the control signal changes the output amplitude of IF amplifier 12. Eventually, this output is applied to power amplifier 14 driving a broadcast antenna 16.
It is desirable to adjust potentiometer P1 and the signal on control terminal C of IF amplifier 12 accurately and often remotely. One known technique involves employing servo motors to drive potentiometer P1 and another motor-driven potentiometer for producing a control signal for the control terminal C. A disadvantage with these known systems is their tendency to overshoot desired settings. Furthermore, noise and backlash in conventional potentiometers can be a problem and may degrade the accuracy of the adjustment.
Accordingly, there is a need for an improved adjustment system and technique wherein the adjustments on an electronic or electrical system can be set accurately, smoothly and without noise.